我正在写一个关于从文件读/写的项目,当我尝试从文件中读取一个对象时遇到同样的问题。我必须打印所有等级为>的学生。 3.00但它没有打印任何东西!有什么建议吗? 附:对不起,我的英语不好 ;) 这是我的代码:
#include<iostream>
#include<fstream>
#include<cstring>
#include<algorithm>
#include<queue>
const int MAX_SIZE = 35;
using namespace std;
class Student {
char name[MAX_SIZE];
double mark;
int phone_number;
public:
Student(char const* _name = "anonimous", double = 2, int = 0);
char const* getName() const { return name; }
int getMark() const { return mark; }
int getPhone() const { return phone_number;}
void setMark(double newmark) { mark = newmark; }
void setPhone(int newphone) { phone_number = newphone; }
friend istream& operator>>(istream& is, Student& s);
friend ostream& operator<<(ostream& os, Student const& s);
bool operator>(Student const& s) const;
bool operator<(Student const& s) const;
void mycopy(Student const& s){
strcpy(name,s.getName());
mark = s.getMark();
phone_number = s.getPhone();
}
};
Student::Student(char const* _name, double _mark, int _phone_number)
:mark(_mark), phone_number(_phone_number){
strncpy(name, _name, MAX_SIZE);
name[MAX_SIZE] = '\0';
}
istream& operator>>(istream& is, Student& s){
return (is >> s.phone_number >> s.mark).getline(s.name,MAX_SIZE);
}
ostream& operator<<(ostream& os, Student const& s){
return os << "Name: "<<s.name<<" Grade: "<<s.mark<<" Phone: "<<s.phone_number<<endl;
}
bool Student::operator>(Student const& s) const{
return name > s.getName();
}
bool Student::operator<(Student const& s) const{
return name < s.getName();
}
Student* readStudent(int n){
Student* s = new Student[n];
for(int i=0;i<n;i++){
cin >> s[i];
}
return s;
}
void writeStudent(Student* s, int n){
ofstream fo("my_database.txt");
for(int i=0;i<n;i++){
fo << s[i];
}
}
int main(){
Student* students = new Student[10];
students[0] = Student("Ivan Petrov",4.25,359887954521);
students[1] = Student("Marina Popopva",5.75,359897254521);
students[2] = Student("Petar Ivanov",3.15,359888845723);
students[3] = Student("Stilqn Petrov",2.65,359895745812);
students[4] = Student("Ivelina Veselinova",3.20,359878745861);
students[5] = Student("Margarita Ivanova",4.50,359885421457);
students[6] = Student("Boqn Pavlov",6.00,359898632541);
students[7] = Student("Iliqn Karov",3.00,359878389699);
students[8] = Student("Ivan Dobromirov",4.18,359886574287);
students[9] = Student("Georgi Lubenov",5.61,359885749354);
writeStudent(students,10);
ifstream sf("my_database.txt");
Student s;
while( sf >> s){
if (s.getMark() > 3.00){
cout << s << endl;
}
}
return 0;}
答案 0 :(得分:2)
有几个问题:
int getMark() const { return mark; }
应该返回double
,而不是int
students[0] = Student("Ivan Petrov",4.25,359887954521);
您的电话号码大于int
,如果需要以0
开头,该怎么办?应该是std::string
而不是
检查您的::operator>>
和<<
。它们不一致:
您的operator<<
:
ostream& operator<<(ostream& os, Student const& s){
return os << "Name: "<<s.name<<" Grade: "<<s.mark<<" Phone: " <<s.phone_number<<endl;
}
将导致数据线看起来像这样:
姓名:Ivan Petrov等级:4.25电话:359887954521
然后是你的operator>>
:
return (is >> s.phone_number >> s.mark).getline(s.name,MAX_SIZE);
错了。你需要阅读并忽略一些字符串。我建议您使用std::string
来存储名称。这是一个假定使用的实现:
istream& operator>>(istream& is, Student& s){
std::string firstName;
std::string lastName;
std::string tmpStr;
is >> tmpStr; // "Name: "
is >> firstName;
is >> lastName;
s.name = firstName + " " + last_name; // consider even storing these in separate fields
is >> tmpStr; // "Grade: "
is >> s.mark;
is >> tmpStr; // "Phone: "
is >> s.phone_number;
return is;
}
其他事项:
Student* students = new Student[10];
无需使用新的:Student students[10];
尽量避免硬编码&#34; database.txt&#34;作为输入/输出文件。将文件名作为函数的参数。
答案 1 :(得分:0)
我看到的问题:
输出和输入功能不对称。你有:
istream& operator>>(istream& is, Student& s){
return (is >> s.phone_number >> s.mark).getline(s.name,MAX_SIZE);
}
ostream& operator<<(ostream& os, Student const& s){
return os << "Name: "<<s.name<<" Grade: "<<s.mark<<" Phone: "<<s.phone_number<<endl;
// "Name: " and " Grade: " are extra data.
}
当std::string
类型的变量中包含空格时,operator<<()
函数会将空格写入输出流,但operator>>()
将停留在第一个空白字符处。因此,你用
os << s.name
与
中的内容不同is >> s.name
您需要更改策略以保存名称。
在保存名称之前先保存名称的长度。在阅读数据时,请先阅读长度,然后再阅读名称。
您没有保存mark
。你也不是在读它。
这是我对功能的建议。
istream& operator>>(istream& is, Student& s){
// Read the size.
size_t size;
is >> size;
// Read the space and discard.
is.get();
// Now read the name.
is.read(s.name, size);
// Null terminate the string.
s.name[size] = '\0';
// Read the phone number
is >> s.mark;
// Read the phone number
is >> s.phone_number;
return is;
}
ostream& operator<<(ostream& os, Student const& s){
// Write the size.
size_t size = strlen(s.name);
os << size;
// Write a space as a separator.
os << " ";
os.write((char*)s.name, size);
// Write a space as a separator.
os << " ";
// Write the mark.
os << s.mark;
// Write a space as a separator.
os << " ";
// Write the phone number.
os << s.phone_number;
return os;
}